The Structure of the Cyclodextrin Complex. XI. Crystal Structure of Hexakis(2,3,6-tri-O-methyl)-α-cyclodextrin–p-Iodoaniline Monohydrate

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Abstract
The crystal structure of hexakis(2,3,6-tri-O-methyl)-α-cyclodextrin–p-iodoaniline complex, C54H96O30·C6H6NI·H2O, was determined by the X-ray method. The crystal is monoclinic with the space group P21, Z=2, a=11.440(4), b=23.674(6), c=13.531(3) Å, and β=91.90(2)°. The structure was solved by the heavy atom method combined with the rigid-body least-squares technique and refined by the block-diagonal least-squares method to the final R-value of 0.11 for 2186 reflections (sinθ⁄λ<0.49). Hexakis(2,3,6-tri-O-methyl)-α-cyclodextrin is in the shape of a truncated elliptical cone; these cones are stacked along the a axis to form a channel-type structure. The guest p-iodoaniline and water molecules are located in the channel. The iodophenyl group is inserted rather loosely from the base side of the truncated cone. The iodine atom is located at the center of the cavity, while the amino group outside the host cavity forms a hydrogen bond with the water molecule. The water molecule is also hydrogen bonded to the adjacent host molecule along the channel. The crystal is built up of columns of the host molecules, which are closely packed in the van der Waals contact.